The H44 antibody reacts with the interleukin-18 receptor alpha chain, also known as IL-1Rrp, an IL-1R family member. IL-18R alpha is expressed on Th1 cells, NK cell subset, neutrophils and IL-12-stimulated tonsillar B cells. By itself, IL-18R alpha binds IL-18 with low affinity and when complexed with IL-18R beta chain binds IL-18 with high affinity. The proinflammatory cytokine IL-18 and its receptor complex play an important role in the innate and autoimmune responses.